Really? Why do cops carry open then?
Concealed is retarded unless you're trying not to make stupid leftist authoritarians whine.
For the same reason the military does. It makes it easier to draw and use their weapons.
Fact is, the public expects the police and military to openly carry their weapons. They do not expect the public to do so for the most part (Security guards, armored car people, etc would be the exception to that.)
Most people who carry a weapon do so for self defense, not as a 'show of force'. There are times and places for both, but usually concealed makes more sense and provides a good balance between protection and not alarming people who may not understand the right to openly carry.
I am a concealed weapons permit holder and I do carry my weapon 99% of the time where its legal for me to do so.